Abstract
A reciprocating extrusion process has been developed for producing Pb-50 vol.-%Sn bulk alloys with fine and uniform microstructures. Two starting materials were used. One was made up of alternately stacked layers of pure Pb and Sn, and the other was cast billets with the same composition. The microstructural evolution as a function of the number of extrusions for these starting materials was investigated and compared. As the number of extrusions increased, the mixing and refining were found to start from the container wall side and die side, and then extended towards the inner core and ram side. The characteristic widths of the Pb and the Sn phases in both starting materials decreased rapidly in the first few passes and then approached the same value. Furthermore, both cases had a similar phase size limit and morphology in which the Pb and the Sn phases formed mutually intervening skeletons beside some isolated islands. The limiting phase width could be explained by the grain boundary sliding mechanism which has been used to explain the high strain rate superplasticity. © 1999 IoM Communications Ltd.